Java Abstract Classes Flashcards

Questions and Answers

Which of the following statements is true concerning abstract classes in Java? (Select all that apply)

An abstract class can be used to instantiate an object of its own by using the new operator.

Constructors can be abstract.

All abstract methods declared in an abstract class must be defined inside the same abstract class.

An abstract class can be used to create an object reference (reference variable). (correct)

In Java, a class can implement multiple interfaces.

True

If you define an abstract class called MyClass (with 2 data fields) in Java that is inherited by a class called AnotherClass, how many AnotherClass objects are instantiated in the heap once the following statement is executed: MyClass [] mc = new AnotherClass ?

0 (correct)

An abstract class may be defined without any abstract method.

<p>True</p> Signup and view all the answers

In the following inheritance-chain diagram, a non-static, and non-final public method in Class_1 can be overridden in Class_3.

<p>True</p> Signup and view all the answers

Study Notes

Abstract Classes in Java

An abstract class cannot have abstract constructors, thus option A is incorrect.
Abstract classes allow the creation of an object reference (option B is correct).
It is not possible to instantiate an abstract class directly using the new operator (option C is incorrect).
Not all abstract methods need to be defined in the same abstract class, so option D is incorrect.

Interfaces in Java

A class can implement multiple interfaces, demonstrating Java's support for multiple inheritance through interfaces.

Object Instantiation in Inheritance

If an abstract class MyClass is extended by AnotherClass and the statement MyClass[] mc = new AnotherClass; is executed, 0 AnotherClass objects are instantiated in the heap.

Abstract Class Flexibility

An abstract class can exist without any abstract methods, allowing for flexible design even without enforcing method implementations.

Method Overriding in Inheritance

In inheritance chains, a non-static, non-final public method in a base class can be overridden by a subclass, indicating the dynamic nature of method resolution in Java.

Description

Test your knowledge on abstract classes in Java with these flashcards. Learn about constructors, object references, and method definitions specific to abstract classes. Perfect for anyone looking to solidify their understanding of this important Java concept.